The present invention relates generally to an apparatus and method for monitoring a refrigeration system and, in particular, to an apparatus and method for sensing and indicating a low refrigerant condition in a refrigeration system.
In typical refrigerators, a refrigerant is repeatedly cycled alternately liquefying by condensation and gasifying by evaporation within a refrigeration circuit. A refrigerator will cool an enclosed area by removing heat from the air therein with an evaporator after the liquid refrigerant is gasified by passing through an expansion valve. Refrigerators are provided with a refrigerant compressor which compresses the low pressure vapor evaporated refrigerant into a high pressure superheated vapor form which is discharged to a condenser for removal of the heat and liquefying.
If the refrigerant leaks from the refrigeration circuit causing a reduction in the amount of the refrigerant in the circuit, the compressor will likely overheat. Particularly, in the event misty oil included in the refrigerant is expected to function as a lubricant the compressor will undergo a lubrication shortage causing a seizure of the compressor. To prevent a compressor seizure, the operation of the compressor must be stopped when the refrigerant leaks below a predetermined safety level. Three known ways of sensing refrigerant loss are: 1) to sense the refrigerant temperature, which rises in response to a decrease in the amount of refrigerant; 2) to sense the temperature of an oil pan disposed in the bottom portion of the compressor to detect a decrease of the enclosed refrigerant; and 3) to observe bubbles in a sightglass located in the liquid line of a refrigeration system. When a sightglass is utilized, such an observation can be misleading as flash gas bubbles occur even when the refrigeration system is not low on refrigerant.
A variety of known refrigeration monitoring systems measure the temperature of the refrigerant to detect a low refrigerant condition. U.S. Pat. No. 3,415,070 discloses a refrigeration warning system having a chamber surrounding a refrigerant liquid header connected between a condenser and a refrigeration unit evaporator. A small amount of the refrigerant entering the header is diverted to the chamber. When the supply of liquid refrigerant is reduced, a temperature rise in the top of the chamber caused by the presence of gas rather than liquid is detected by an externally mounted temperature sensor for energizing an alarm.